The present invention generally relates to water separation systems and, more particularly, to apparatus and methods for coalescing water and removing odors from air.
Low concentrations of odiferous compounds frequently contaminate aircraft cabin air. The most likely sources of such odors are engine oil, hydraulic fluid, and rub seal. As such, the odor causing molecules are probably high molecular weight decomposition products of the foregoing materials. One solution for odor control is the treatment of contaminated air with activated carbon filters. While treatment of odors with activated carbon has a long history of application, little has been done in the context of high humidity, cold air environments such as those found in aircraft low-pressure water separator systems.
A typical low pressure water separator system processes low temperature, high humidity air exiting the aircraft air conditioning system. The original purpose of the water separator, as its name implies, is to remove entrained liquid water from the water saturated air stream. This is accomplished in three steps: first coalescence of water droplets on a coalescer "bag" filter; then a centrifugal separation step which spins the water droplets away from the air stream into the water collector area or sump of the separator; and then water is removed from the sump by venting to the atmosphere.
An example of using activated carbon to remove odors is found in U.S. Pat. No. 3,857,732. A conventional non-woven fabric has its fibers coated with a water insoluble composition that can include activated carbon. Alternatively, a pasty mass having activated carbon can be impregnated into the fabric. Similarly, U.S. Pat. No. 5,744,236 discloses a non-woven media of fibers made of polyamides, polyesters, or polyolefins. Activated carbon is entrapped within the hollow cavities of the fibers in the absence of an adhesive to thereby adsorb odor molecules. However, the foregoing only describe the ability to remove odors from air, not the ability to also remove water that can be present in aircraft cabin air, for example.
A non-woven activated carbon fabric is shown in U.S. Pat. No. 4,565,727 for the use of protective clothing, although air conditioning filters were also contemplated. The fabric is prepared by wet-laying the activated carbon with fibrillated acrylic fibers. Thereby, toxic compounds are absorbed and water vapor (such as perspiration) permeates through the fabric. Of course, since water vapor permeates, the fabric is not removing water.
A filter that not only removes odors but also absorbs water is described in U.S. Pat. No. 5,783,080 wherein the filter is prepared with a first catalyst (such as hydrochloric acid), a second catalyst (such as formalin), a vegetable starch, a liquid non-particle polyvinyl alcohol, and active carbon. The foregoing is coated on a plate fiber that has percolating holes that serve to absorb water. A subsequent drying step is required to remove the absorbed water from the filter. Accordingly, a disadvantage to this filter is the need for additional processing for water removal. In addition, the technique described in this disclosure requires the use of a binder to immobilize the carbon onto the support substrate, and consequently loss of activity of the activated carbon can be expected.
Another filter that is described as having the ability to remove water vapor and odor from air is in U.S. Pat. No. 4,130,487. In one embodiment of the filter, two pleated sheets of laminated filter media include glass fibre filter paper bonded to a filter material or paper. The pleated sheets are supported at their interior and exterior surfaces by cylinders of expanded metal. This filter is claimed to remove water mist from an air stream, although no evidence of this ability is presented nor is the concept of water droplet coalescence mentioned. The process, as described, treats water or oil droplets as particulate contaminates, and there are apparently no provisions which show how the described process can result in the coalescence of water droplets into a bulk fluid which is gathered into a sump for later removal by draining. In another embodiment, a pleated sheet of an activated carbon layer and a paper filter media layer is provided between two cylinders of expanded metal for support. The filter media layer includes a glass fiber filter paper bonded to a filter material or paper. The carbon layer is outside of the filter media layer. The carbon layer adsorbs gases and the filter layer removes particulate matter, although neither apparently removes water vapor. In both of the two embodiments, air flows from outside to the inside of the filter. Disadvantages, however, to this design include vast complexity in design, and the inability to handle saturating levels of water in the incoming process air stream. This is evidenced by the lack of a means to remove excess water than will inevitably build up in the filter system.
As can be seen, there is a need for an improved filter and method that not only removes water but also odors from an air stream. A filter and method is needed that can operate in conjunction with a low pressure water separator system in, for example, aircraft. A further need is for a filter and method that coalesces water and removes odors from an air stream at a low temperature and high humidity. An additional need is for a filter and method that removes water and odors from air moving at a high velocity. A filter and method of coalescing water and removing odor from an air stream is needed that is simple in design and can easily serve as a retrofit to existing environmental control systems, such as ones that provide an air supply to a cabin of an aircraft.